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- // +build amd64,!noasm
-
- #include "textflag.h"
-
- // Digits of 3^238 - 1
- #define THREE238M1_0 $0xedcd718a828384f8
- #define THREE238M1_1 $0x733b35bfd4427a14
- #define THREE238M1_2 $0xf88229cf94d7cf38
- #define THREE238M1_3 $0x63c56c990c7c2ad6
- #define THREE238M1_4 $0xb858a87e8f4222c7
- #define THREE238M1_5 $0x254c9c6b525eaf5
-
- // Set result to zero if the input scalar is <= 3^238, otherwise result is 1.
- // Scalar must be array of 48 bytes
- // func checkLessThanThree238(s_base uintptr, s_len uint, s_cap uint) uint8
- TEXT ·checkLessThanThree238(SB), NOSPLIT, $0-16
- MOVQ scalar+0(FP), SI
-
- XORQ AX, AX
-
- // Set [R10,...,R15] = 3^238
- MOVQ THREE238M1_0, R10
- MOVQ THREE238M1_1, R11
- MOVQ THREE238M1_2, R12
- MOVQ THREE238M1_3, R13
- MOVQ THREE238M1_4, R14
- MOVQ THREE238M1_5, R15
-
- // Set [R10,...,R15] = 3^238 - scalar
- SUBQ (SI), R10
- SBBQ 8(SI), R11
- SBBQ 16(SI), R12
- SBBQ 24(SI), R13
- SBBQ 32(SI), R14
- SBBQ 40(SI), R15
-
- // Save borrow flag indicating 3^238 - scalar < 0 as a mask in AX (rax)
- ADCB $0, AX
- MOVB AX, ret+24(FP)
-
- RET
-
- // Multiply 48-byte scalar by 3 to get a scalar in 3*[0,3^238)
- TEXT ·multiplyByThree(SB), NOSPLIT, $0-8
- MOVQ scalar+0(FP), SI
-
- // Set [R10,...,R15] = scalar
- MOVQ (SI), R10
- MOVQ 8(SI), R11
- MOVQ 16(SI), R12
- MOVQ 24(SI), R13
- MOVQ 32(SI), R14
- MOVQ 40(SI), R15
-
- // Add scalar twice to compute 3*scalar
- ADDQ R10, (SI)
- ADCQ R11, (8)(SI)
- ADCQ R12, (16)(SI)
- ADCQ R13, (24)(SI)
- ADCQ R14, (32)(SI)
- ADCQ R15, (40)(SI)
- ADDQ R10, (SI)
- ADCQ R11, (8)(SI)
- ADCQ R12, (16)(SI)
- ADCQ R13, (24)(SI)
- ADCQ R14, (32)(SI)
- ADCQ R15, (40)(SI)
-
- RET
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